Ore dressing jig



Oct.' 25, 1938.

H. H. SMITH 2,134,154

ORE DRESSING JIG Original Filed June 25, 1952 V I z II"I :i A

DOWN STROKE 41 Hays Patented Oct. 25, 1938 UNITED STATES ORE. DRESSING JIG Harold .Hardy Smith, Parkview, Johannesburg, Union of South Africa, assignor of three-fourths to General Mining & Finance Corporation, Limited, Johannesburg, Union of South Africa Application June 25, 1932, Serial No. 619,309. ,Re-

newed July 15, 1937. In the Union of South Africa July 27, 1931 6 Claims. (01. 209 425) The present invention relates to jigs for concentrating ores and other materials.

The principal object of the invention is to construct a jig adapted for a large capacity per unit of screen area, with a good recovery of the finer concentrates and low dilution of the tailing, and capable of handling a feed containing a wide range of particle sizes.

The pulp travelling over a sieve bed from the feed point to the point of discharge tends to increase in bulk due to the additions of hutch water through the bed; andif such increase of bulk results in largely increased velocity of flow over the bed, fine valuable particles are prevented from settling and are lost.

Such increase of velocity and resulting loss can be minimized by making the sieve in the shape of a buddle, with feeding means at the centre and peripheral discharge of the tailings; but in the few known instances where this arrangement has been proposed it was embodied in constructions which were inherently incapable of large outputs and clean concentration.

According to one aspect of the present invention, dilution of'the tailing by hutch water is minimized and rapid movement of the material over the bed together with high grade hutch concentrate is attained by constructing a jig with a circular sieve which is vertically reciprocated, is fed at the centre, and discharges the tailings at its periphery.

The invention provides a head motion for the sieve such that, in each reciprocation, said head motion moves the sieve downward with constant acceleration approaching a point beyond half the stroke, at which it attains its maximum velocity,

then said head motion suddenly retards it and reverses it into the upstroke so that it attains its maximum velocity at less than half the stroke,

and said head motion then moves it with constant deceleration toward the top of its stroke, the movement in each reciprocation being purely vertical.

The invention further provides a fluid tight seal between a vertically reciprocating jig sieve and the hutch; as 'by means of a rubber or other flexible strip having its edges secured respectively. to said parts. In this way interference with the results last described, by leakage of water or air between the sieve and the hutch, is avoided; whilst in the case of a circular sieve discharging tailings at its edge, contamination of the hutch product by the tailings is definitely avoided.

A jig constructed according to the invention is shown in the accompanying drawing in which I Fig. I is a vertical section.

Fig. II is an enlarged plan of a part of the ad justable sieve rim.

Fig. III is a detached View of the head motion.

7 Fig. IV is a diagram relative to the head motion.

r The hutch consists of the conical vessel 2- having any appropriate outlet for concentrates such as the goose-neck 3 extending from its lower part.

Around the top of the hutch is the annular tailings collecting launder 4 having an outlet'5.

The sieve comprises a spider consisting ofa boss 6 and arms I: the circular upper and lower grids 8, 9 resting on and secured to the spider; and the circular screen 10 between the grids. The jig illustrated is intended to deliver concentrate only through the sieve, the'bed accordingly consists of a lower layer II of ragging and an upper layer l2 of ore. The ragging is retained in position by the cells of the upper grid 8. The similar cells of the lower grid 9 constrain the water currentsfor vertical movement.

The sieve is provided with a raised rim 13 to retain the ore column l2. For adjusting the depth of the ore column there is shown a'supplementary rim adapted to be clamped to the rim l 3 so as to project to the desired height above the latter. It comprises several arcuate sections l4 (Figs. I and II) provided at their adjoining ends with lugs I5 and clamp bolts l6 bywhich the sections. are drawn together to clamp onto the rim [3. Between the lugs are soft rubber or like filling pieces I! which close the gaps between the lugs I5 and so prevent ore from escaping through.them, whilst allowing the lugs tobe adjusted towardsone another. I r

A surge grid l8 isfixed in the hutch immediately below the sieve to prevent surging of the hutch water between the inner and outer areas of the sieve.

I9 is a strip of rubber secured at its edges respectively to the rim 'of the sieve and to the inner rim of the launder 4, and making a fluid tight seal between the sieve and the hutch. It is desirable to minimize as far as possible the tendency of the strip 19 to act as a water-plunger, since such plungeraction tends toupset the action of the reciprocating sieve. The strip l9 should therefore approximate to a vertical position, but such position often involves practical disadvantages, and it has been found that if, when fully extended, the strip makes an angle to thehorizontal of not less than aboutthirty degrees, it

cated vertically. The head motion comprises the toggle links 25, 26, the former of which rests at H its lower and outer end upon a block 2| supported on a fixed part 28; and the latter of which carries on its upper and outer end the cross bar 24 of the cross head. The outer end of the upper link-26 is in the axial line of the sieve and the shaft 2|. By means of the screw 29 which shifts the block 21 horizontally, the outer end of the lower link can be adjusted to be in the same axial line as shown or to the left of said axis. A rod 30 extending upward from the cross head engages a guide 3| to counteract the side thrust of the toggle.

The inner ends of the toggle links engage a pitman 32 which is reciprocated endwise by an eccentric 33 on the shaft 34. The pitman lies approximately 'at an angle of ninety degrees to the toggle but the shaft bearings 35 are adjustable vertically on their fixed support, to enable such angle to be varied. The shaftis rotated as by abelt pulley 35 and is fitted with afiy-fwheel 31 for maintaining regularity of rotation. Contact between the bar 24 and the toggle is maintained by'springs 38 compressed between a fixed member 39 and the cross-arm 4|! on the shaft 2|. The tension spring, thecompressionsprings 38 and the reci rocating partsrenresented main: ly by the sieve, form a system adapted for vertical oscillation with a natural frequency: and when forcibly displaced from its neutral position and released. would continue'to oscillateunt l stopped by friction." The head rnotion therefore'has merely to maintain the reciprocation by making up friction lossesand is not called upon tofsustain the weight of the sieve." It has'only to govern the accelerations and decelerations of the sieve and not to provide thelwhole of the force neces: sary for each such operation. The natural frequency of reciprocation of the system depends principally ron the mass of the loadedh sieve and the upward and downward pressure of the respective springs. By making the spring pressures sufiiciently great relatively to the mass, the natural frequency of the system may be made as high as desired; that is, rapid reciprocation of the sieve may be attained without unduly stressing the head motion. Such rapid reciprocation permits of a large number of short strokes per unit of time; so giving ahigh throughput, and also ensuring that the bed is left open or in suspension 'when the upward stroke of the'sieve begins. The tension spring'4l has an adjustment 42 to compensate for varying weight of the bed l2.

The arrangement is such that the toggle oscillates between the-broken position of Fig; I and the Fig. III position in which the links are more nearly alined' with one another. The result is that the sieve is reciprocated vertically between its lowered position of Fig. I and. its raised position of Fig. III, with a motion which is characterized by "substantially constant downward acceleration approaching a point more than half the downward stroke, sudden retardation, and rapid reversal to upward motion; The machine'has been constructed with the following dimensions, viz:+

Inches Length of lower toggle link 25 10% Length of upper toggle link 24 6% Thickness of pitman between links 3 Effective length of pitman 12 Eccentric stroke 1% 7 Centre of shaft 34, inch below the mid point between the adjacent ends of the toggle links when the mechanism is in the Fig. III position.

Such mechanism produced a sieve motion represented by the graph Fig. IV where abscissae represent time and ordinates represent sieve velocity. The point A of the graph corresponds with the commencement. of the downward stroke and point B. lies at about six-tenths of that stroke. The straight portion of the line approaching point Bindicates'substantially constant increase ofvelocity, whilst the sharp peak at B shows the sudden retardation. The steepness of the line from B to C exhibits the rapid reversal to upward movement and compares with the slowerreversal at the top of the strokershown by the less steep line C. A. B. 1

By shifting the block 21 over to the left, the length of the sieve stroke is increased and the ef fects mentioned above in reference to the graph are intensified.

The pulp to be treated is delivered by apipe 43 into a stationary annular hopper 44 surrounding the shaft 2|. Said feed pipe delivers the pulp tangentially into the hopperso that 'it is well distributed all around the same. The hopper has a bottom discharge in the form of a short pipe 45 which directsthe pulp into, anannular receiving trough 46'on the sieve.

Water is supplied to the hutch from an open tank 41 in which'a predetermined water level is maintained as by a ball valve 48. Such level may be varied by adjusting the ball up or down the threaded spindle 49. -A pipe 50 leads from the tank to a point in the'hutch' where the cross section is large so that the inflow does not interfere withthe settlement of the concentrates; being provided with a conical'cover 5| to prevent concentrates from falling into it from the sieve.

-A non-return valve 52 in the pipe line prevents water being returned from the hutch to the cistern by the pulsations of the sieve. The pipe 50 is of large diameter to' allow very free movement of water from the tank to the hutch.

In the operation of the device, pulp for concentration is fed from pipe 43' into the hopper 44 which feeds it evenly around the annular trough 46 of the sieve. Owing to the vertical reciprocating movement of the sieve the pulp travels readily towards the periphery of the sieve. The concentrate passes through the bed into the hutch; Whilst the tailing flows over the lip |4 into thetrough 4. The seal 9 prevents the'tailing from leaking into the hutch at this point. For the recovery of fine concentrates such as that from pyritic goldore, a sieve stroke of from M; inch to inch is desirable, with a frequency of about 2'70 to 300 complete'reciprocations per minute. V

The continued acceleration of the sieve during the greaterpart of its downward movement and its rapid reversal keep the bed open for a considerable proportion of each period, thus facilitating movement of the concentrate through the bed and minimizing felting of the bed under conditions of short stroke and little hutch water. The quick return tends to cause hutch water which has entered the bed to be rejected downwardly rather than upwardly, thus diminishing consumption of hutch water. Also the interstitial downward currents which are laregly responsible for drawing the fine grains of valuable mineral out of the ragging into the hutch are set up before compacting of the ragging has jambed the grains and. rendered them immovable.

The level of the water in the tank 41 is so regulated as to check, to the desired extent, the downward interstitial water currents in the bed; such currents, if too intense, tending to carry gangue as well as concentrate into the hutch. The ability to maintain a constant level in the tank 41 and to adjust such level, together with the prevention of leakage by the seal l9, permit such regulation to be accurately effected.

A jig constructed as described with reference to the drawing was arranged to recover pyrite from West Witwatersrand ore. The jig was located in the tube mill circuit and treated the whole of the tube mill discharge after elimination therefrom of plus inch pebbles.

The net sieve area was 45 square feet. The speed was 275 R. P. M. and the stroke inch. The ragging was iron slag from a faggot heating furnace crushed and graded to pass a screen of 0.187 inch square opening and to remain on a sieve of 0.034 by 0.281 inch rectangular opening.

The tonnage treated was 1450 tons of solids per 24 hours; or practically one ton per minute. This tongage is equivalent to 32 tons per square foot of sieve area, per 24 hours.

The total water entering the hutch was 800 lbs. per minute, of which approximately 100 lbs. per minute were discharged with the concentrates and the remaining 700 lbs. passed through the jig bed. This is 700 lbs. of bed water per ton treated, or 15.5 lbs. per square foot of sieve per minute, or 0.25 cubic feet per square foot of sieve per minute. v

The feed pulp coming to the jig contained 41% moisture, and the tailings pulp leaving the jig contained only 51.2% moisture. The concentrate was discharged from the hutch at a dilution of 2.22 lbs of water to each pound of solids (or 69% moisture in the pulp).

The grading analyses of the feed to the jig and of the clean pyrite separated (by means of hand panning) from the jig concentrate were as follows:-

Clean pyrite from jig concentrate percent weight Mesh Tyler }4II+1/II It will be noted that the jig successfully dealt with pulp containing particles of widely difiering sizes, and delivered a concentrate containing 7 high proportion of very fine pyrite.

The pyrite entering the circuit with the tube mill feed was 706 lbs. per hour. The amount of jig concentrate produced was 1.35 tons per hour containing 16% of pyrite, or an output of 432 lbs. of pyrite per hour, representing an extraction of 61.1%.

The solids in the pulp leaving the circuit contained 1.5% of pyrite; mostly fine enough to pass a 200 mesh screen.

I claim:

1. In a jig, the combinationof a circular sieve, an adjustable lip seated on the periphery of the sieve and consisting of a fiat metal band provided with lugs and clamped around the sieve by means of said lugs and yielding filling pieces between the lugs.

2. In a jig, the combination of a circular sieve providing a central circular pulp-receiving trough, means for vertically reciprocating the sieve, a fixed annular feed hopper comprising an annular body and an angular mouth of less diameter than the body positioned above the trough so as to drop pulp into the latter, a tangential pipe for passingv pulp into the body so as to produce a swirling movement therein and means to receive tailing discharging from the circumference of the sieve.

3. In a jig, the combination of a substantially horizontal, vertically reciprocable sieve carrying a mixture of material to be stratified thereen, means for passing liquid upwardly through said screen, and a head motion therefor comprising a rotating shaft, a pitman connected to the shaft for endwise reciprocation, a toggle disposed substantially transversely to said pitman and actuated thereby, said toggle comprising two links extending from opposite sides of the pitman,

one of said links resting at its lower end on a stationary part and the outer end of the other link effecting the reciprocation of the sieve.

4. An apparatus as claimed in claim 3 characterized by the provision of means for adjusting said shaft in a direction about at right angles with the length of the pitman.

5. An apparatus as claimed in claim 3, characterized by the provision of means for adjusting said shaft in a direction about at right an-' gles with the length of the pitman. and means for adjusting the first mentioned link in a direction about parallel with the length of the pitman.

6. The process of concentrating ore and like granular material consisting in forming a jig bed with said material in a body of liquid, reciprocating the bed in said body of liquid and in each reciprocation moving said bed downward with a close approximation to constant acceleration from rest to a point beyond the mid-period of the downstroke stroke, at which it attains its maximum velocity, then suddenly retarding it and. reversing it into the upstroke so that it attains its maximum velocity at less than half the period of the upstroke,-and then moving it with deceleration to the top of its stroke, the movement in each reciprocation being purely vertical.

HAROLD HARDY SMITH. 

